Fruit update - July 16, 2025

Article written by Madeline Wimmer - Extension Educator, Fruit Production

• Apples:
• When should trunk guards be removed from apple trees?
• Check bands, fasteners, and clips to prevent girdling
• Grapes:
• Seasonal update from the UMN HRC
• Kiwiberries:
• Update and about: UMN kiwiberry research and breeding efforts

Apples

When should trunk guards be removed from apple trees?

Images: Two pictures showing tree guards on older trees. One is installed on a central leader trained tree (left) and the other on high-density trained tree (right). 

Trunk guards are helpful for apple tree establishment, as they protect against damage from wildlife and herbicide sprays. But when is the appropriate time to remove them, and what are the consequences of leaving them on too long?

Depending on tree vigor, site conditions, and wildlife pressure, guards can typically be removed once trees are no longer at risk for damage—but they should be checked periodically.

Prolonged use of tree guards can be problematic. For the two images shown above, the tree on the left had moss growth limited to trunk parts located within the trunk guard. This is a sign that the guard was creating a very moist environment. Other issues can develop too, like trunk injury from rubbing against the grow tube as the tree ages and expands.

Like many choices growers face in production, the risks of keeping the guards on should be weighed against the potential risks associated with their removal, like wildlife damage on trees with less wood development. For small orchards, guards can be put on during winter, a high-risk time for wildlife damage, and taken off again in the spring.

Check bands, fasteners, and clips to prevent girdling

Image: Two apple trees trained on high density trellis systems at two different growing sites. Left: the apple tree was fastened to the training wire with a clip that the trunk is currently growing over. Right: The beginning signs of trunk girdling can be seen here from a T-band used for fastening.

During establishment, dwarf and some types of semi-dwarf apple trees benefit from securing trunks onto either training stakes or trellis wires using training supplies. Wire clips provide a simple way to fasten trunks, but need to be checked and eventually removed to prevent trunk damage from girdling, which can be extreme at times, as seen in the above left photo where an apple tree trunk has grown around the trellis wire and clip. 

Rubber T-bands are better able to stretch as the tree ages, but also need to be checked and either removed or replaced with larger bands as the trees grow. When the bands are too tight, they can rub on and wound the adjacent bark, which makes the tree vulnerable to certain pathogens. 

Grapes

Seasonal update from the UMN HRC

Images: The UMN Horticultural Research Center (HRC) grows a number of different varieties, including a few V. vinifera varieties (middle photo) like Chardonnay and Merlot, which are buried each fall to protect against winter injury. Herbicide damage has been high this year throughout the HRC (left photo) and phylloxera has been mostly under control (right photo). 

The University of Minnesota Horticultural Research Center (UMN HRC) focuses heavily on breeding new fruit varieties, primarily breeding and evaluating apples and grapes. I recently checked in with the grape team to hear how their season has been going. 

The following is a seasonal update from grape program leader and researcher: 

“We're seeing higher than normal levels of herbicide drift. Foliar phylloxera pressure is also very high. We started seeing black rot symptoms on both fruit clusters and leaves, especially on highly susceptible materials. The same for downy mildew.* All in all, the frequent rains have been conducive for disease and pest development.”

-Soon Li Teh, UMN Grape Breeder and Researcher

*Most of the disease observations were in the HRC’s block that is not managed with fungicides. Overall, both the grapevine foliage and fruit clusters are looking healthy throughout the vineyard blocks. 

Kiwiberries

Update and about: UMN kiwiberry research and breeding efforts

Images: Actinidia kolomikta (top left and right photos) is grown along with Actinidia arguta (bottom left and right photos) at the University of Minnesota HRC for fruit breeding. Note A. kolomikta’s unique features like its variegated leaves. 

Kiwiberries are an emerging crop for Minnesota growers. The University of Minnesota has researched and led efforts to breed new cultivars to support developing the industry in the past, and that effort is ongoing. Staff at the HRC maintain multiple kiwiberry plots, including the ones pictured in this article section. 

Actinidia arguta and Actinidia kolomikta are the two primary kiwiberry species used in the UMN fruit breeding program (pictured above), which differ in a multitude of ways, including their cold tolerance, vigor, and fruit size. 

The goals for breeding kiwiberries have focused on evaluating new seedlings based on their cold tolerance, pest resistance, nutritional profiles, and reducing actinidin content, which can cause mouth irritation for some people.   

Images: At the UMN HRC, kiwiberries are trained on a pergola style trellis where kiwiberry shoots grow perpendicular to the trellis rows, creating a canopy with fruits that hang beneath. 

Kiwiberries are unique from other fruit crops in their growth and fruiting habits. They are technically bines, which means they bind to structures with their shoots, rather than using tendrils like a grapevine would do. 

The plants can be trained onto a number of different trellis systems. The UMN HRC has one block that is trellised in a quadrilateral layout like a pergola. This type of system requires multidirectional anchoring to maintain the tension in both ways, unlike 2-D trellises, or even linear 3-D trellises used in grape production. 

Kiwiberry bines are trained upward and fastened to trellis poles upon training. From there, shoots can grow out laterally, along the trellis wires, to form cordons from which shoots can grow out perpendicular to the trellis rows (i.e., across one or multiple rows). How much support the plants need depends on their vigor. For instance, A. arguta tends to need more support for how vigorously it grows. 

For growers who are interested in exploring kiwiberries as a crop, take note that these plants are dioecious, meaning that they house their female and male flowers on separate plants. Having one male for every 6–8 females is usually sufficient for pollination needs. 

Kiwiberries are typically harvested later in the summer, during the latter part of the season. One harvest indicator is to open the fruit and look at the seeds. When fruits have fully ripened, their seeds will be dark in color. 

While there are some concerns about the invasive potential of A. arguta in some regions of the U.S., researchers and specialists have not observed much spread. Actinidia continues to be on the Minnesota Department of Agriculture’s invasive species Watch List, but is not regulated. 

Resources and further reading:

Commercial kiwiberry production in Minnesota (University of Minnesota)

A brief history of the kiwiberry in Minnesota (University of Minnesota)

What’s in a kiwiberry? (University of Minnesota)

Thank you to our farm and agricultural professional partners for contributions to the UMN Fruit Update series. Unless otherwise credited, photos were taken by Madeline Wimmer or sourced from the UMN Extension system.

This article may be shared for educational purposes with attribution to the University of Minnesota Extension. For other uses, please contact UMN Extension for permission.